T-CELL REPERTOIRE - GENOMIC OR SOMATIC BIAS TOWARD RECOGNITION OF MAJOR HISTOCOMPATIBILITY COMPLEX-MOLECULES

The prevailing concept about a major influence of thymic positive sele ction on shaping the T cell repertoire during ontogeny is confronted w ith an old idea emphasizing a dominant role for genetic (evolutionary) factors in molding the recognition potential of mature T cells. Our r ecent results are not readily interpreted without introducing a new ve rsion of the old concept, according to which complementarity to the ma jor histocompatibility complex peptide-binding site is a major evoluti onary selective pressure on T cell antigen receptor variable genes, wi th alloreactivity being a reflection of this fact.